Cork or No Cork? The Science of Sealing Wine Bottles

 

Courtesy of Stelvin

Screwcaps create a tighter seal than natural cork.

Supporters of screwcaps argue that, although slight oxidation may flatten some of the harsher notes of a young wine, it does nothing to develop the depth or complexity that bottle aging is supposed to produce. They insist that, if a wine takes longer to reach its peak under a screwcap, that peak will be higher.

Peter Godden of the Australian Wine Research Institute says, "While there is no evidence that any oxygen is required for the reactions we think of as 'wine development', and many such reactions clearly need no oxygen, the presence of oxygen may speed up 'development'." Stelvin, bizarrely claims that "everybody knows" wines mature more quickly with more oxygen (everybody, apparently, aside from screwcap cheerleaders such as the New Zealand Screwcap Initiative, who repeat ad nauseam that oxygen is not involved in wine maturation.

The smell of aging

Some experts argue that the greater (but still tiny) amount of oxygen transmitted by natural cork is needed to prevent reduction problems. Wine can contain sulfides, and with extremely low oxygen concentration, like when a screwcap is used, these sulfides can reduce to compounds called thiols, some of which smell rubbery or flinty. In the presence of slightly more oxygen, this does not happen.

The response from the screwcap lobby is that the presence of thiol precursors (chemicals that can turn into thiols) in wine is a fault, since they should be removed using copper sulphate before bottling. Winemakers have lined up on both sides - some insisting they have followed all the correct procedures and still encountered problems, while others proudly state that their screwcap experiments have been great successes. Californian winemaker Randall Grahm says, "My sense is that for any competent winemaker this is no biggie."

Some experts predict that "designer" screwcaps will eventually become the norm for premium wines, allowing the winemakers to specify the level of oxygen transmission allowed by the closure post-bottling, just as they can control the winemaking process before the wine is bottled.